1. Field of the Invention
This invention relates generally to a door opening device used in a food storage apparatus with a door held in a closed state by a magnet gasket, and more particularly to such a door opening device suitable for household refrigerators having large-sized doors.
2. Description of the Prior Art
Sizes of food storage apparatuses such as household refrigerators have recently been increased. With this increase, sizes of doors closing and opening respective storage compartments of the refrigerator such as a refrigerating compartment have also been increased. Each of the doors of the refrigerator includes a magnet gasket generally provided along a peripheral edge of the backside or inside thereof. The door is held in a closed state by a sticking force of the magnet gasket. Accordingly, the overall length of the magnet gasket is increased with the increase in the size of the door of the refrigerator and a force required for opening the door is accordingly increased.
To reduce the force required for opening the door, the prior art has proposed devices employing electric driving sources for pushing a push rod which further pushes the door in its opening direction. One of the proposed door opening devices employs an electric motor as the electric driving source. Torque developed by the motor is transmitted through a gear mechanism to a pinion. Rotation of the pinion is converted via a rack into a linear motion of the push rod. However, the motor-driven type door opening device has a problem of low-speed operation of the push rod.
On the other hand, an electromagnetic solenoid has been proposed as the driving source of the door opening device. The push rod is moved with a plunger upon energization of the electromagnetic solenoid. The plunger can momentarily be moved in the solenoid type door opening device. The push rod requires a sufficiently large movement stroke in order that the door may be opened reliably. However, a movement stroke of the plunger has not sufficiently been increased in the electromagnetic solenoids of the conventional type. Furthermore, the conventional electromagnetic solenoids produce noise due to collision during attraction by the plungers. It has been difficult to reduce the noise.
Therefore, an object of the present invention is to provide a door opening device for food storage apparatuses in which the operating force required to open the door against the adsorbing force of the magnet gasket can be reduced, the door can be opened reliably, and noise due to the door opening operation can be reduced.
The present invention provides a door opening device which is mounted on a food storage apparatus including a body with a storage compartment, a door for opening and closing an opening of the storage compartment, and a magnet gasket holding the door in a closed state. The door opening device comprises a generally cylindrical coil unit provided on the body of the food storage apparatus and having an axially extending through hole, a plunger provided in the hole of the coil unit so as to be axially moved with respect to the coil unit, the plunger being moved in one direction when the coil unit is energized, the plunger having two axial ends, and a pushing member provided on one axial end of the plunger so as to be moved with the plunger, the pushing member pushing the door in an opening direction against a sticking force of the magnet gasket when moved in said one direction with the plunger.
According to the above-described construction, the door of the storage compartment is opened by a pushing force of the pushing member. Consequently, a force required to open the door can be reduced. Further, the plunger is provided in the hole of the coil unit so as to be axially moved with respect to the coil unit. Consequently, since the movement stroke of the plunger is sufficiently increased, the door can be opened reliably.
The coil unit preferably includes a bobbin having the through hole, a coil wound on an outer periphery of the bobbin, a generally rectangular frame-shaped yoke assembly enclosing the bobbin and the coil, and a cylindrical auxiliary yoke provided in the through hole of the bobbin so as to come into contact with the yoke assembly. The auxiliary yoke can increase the attractive force produced upon energization of the coil unit.
The door opening device preferably further comprises a return spring urging the plunger in the other direction. Upon deenergization of the coil unit, the urging force of the return spring moves the plunger and the pushing member toward the former positions. Consequently, the pushing member can be prevented from being held in a state where it projects ahead of the front of the body of the storage apparatus.
The pushing member preferably has a distal end which abuts against the door while the door is in a closed state. This construction clearly differs from the construction in which the pushing member is moved upon energization of the coil unit to thereby collide against the door. As a result, noise produced during the opening of the door can be reduced.
The door opening device preferably further comprises a pushing spring urging the pushing member in said one direction so that the distal end of the pushing member abuts against the door. As the result of this construction, the distal end of the pushing member can reliably abut the door when the door is in the closed state. Furthermore, the pushing spring preferably pushes the other end of the plunger to thereby urge the pushing member in said one direction. The pushing spring serves as a buffer receiving a return force of the plunger. Consequently, occurrence of noise can be restrained when the plunger is returned.
The door opening device preferably further comprises a compression coil spring wound on a portion of the plunger protruding toward the other end side relative to the hole. In this construction, the compression coil spring has two ends fixed to said other ends of the plunger and the coil unit respectively. The compression coil spring serves as a pushing spring urging the pushing member in said one direction so that the distal end of the pushing member abuts against the door and as a return spring urging the plunger in the other direction. Thus, a single compression coil spring has two functions and accordingly, the number of parts can be reduced.
The door opening device preferably further comprises a rectifier circuit rectifying output of an AC power supply, a smoothing capacitor smoothing the rectified output, and a DC power supply circuit supplying DC power to the coil unit to drive the same. In this construction, electric charge of the smoothing capacitor is discharged through the coil unit after deenergization of the coil unit so that the plunger is braked while being returned by the return spring. The load current of the coil unit is supplied through the smoothing capacitor. As a result, occurrence of electromagnetic sound due to pulsation of the load current can be prevented. Further, since the plunger and pushing member are returned slowly, the noise due to the return of the plunger can be reduced.
The door opening device preferably further comprises a timer circuit limiting an energizing period of time of the coil unit to or below a predetermined value. Since the coil unit is not energized for an excessively long period of time, an abnormal increase in the temperature of the coil unit can be prevented. Furthermore, the coil unit is preferably mounted on a member further mounted directly on the body of the storage apparatus. The vibration is difficult to transfer to the body of the storage apparatus even when the coil unit is caused to vibrate. Consequently, the vibration can be prevented from being amplified at the body side into a loud noise.
The door opening device preferably further comprises a thermal fuse adhering closely to a surface of the coil unit so as to be melted, thereby cutting off power to the coil unit, and a covering member holding the thermal fuse in an adherent state to the surface of the coil unit and covering the thermal fuse, the covering member being made of a resin. In this construction, an accurate temperature of the coil unit is transferred to the thermal fuse. As a result, a current path for the coil unit can reliably be cut off by the thermal fuse when the temperature of the coil unit is abnormally increased.
The door preferably has two opposite ends and is preferably hingedly mounted at one of the ends of thereof on the body of the storage apparatus so as to pivot and the pushing member pushes a portion of the door between a horizontally middle thereof and the other end thereof. Consequently, a force required to open the door can be rendered smaller. Further, the door preferably includes a pushed portion provided outside the magnet gasket thereon, the pushed portion being pushed by the distal end of the pushing member. In this construction, the device further comprises a buffing member provided on at least one of the distal end of the pushing member and the pushed portion. Although the door is pushed by the pushing member, this construction does not affect the effective capacity of the storage compartment. Additionally, the shock due to the pushing operation of the pushing member against the door can be reduced.
The body of the storage apparatus preferably has a top on which the coil unit is disposed so that a part thereof is positioned inside the body. This construction can prevent an increase in the height of the body of the storage apparatus.
The door opening device preferably further comprises a controller which controls energization to the coil unit according to a temperature of the coil unit. Thus, the controller can prevent an abnormal increase in the temperature of the coil unit and accordingly, the safety of the door opening device can be improved.
The controller preferably estimates the temperature of the coil unit on the basis of a previously set temperature change rate. This arrangement requires no temperature detecting means for detecting the temperature of the coil unit. As a result, the arrangement of the door opening device can be simplified. Further, the coil unit preferably includes a coil, and the controller measures a resistance value of the coil to thereby detect the temperature of the coil unit. Consequently, the temperature of the coil unit can be detected accurately.
The controller preferably prohibits energization of the coil unit when the temperature of the coil unit reaches a predetermined prohibition temperature, and the controller permits re-energization of the coil unit when the temperature of the coil unit decreases to a predetermined permission temperature. This arrangement can prevent an abnormal increase in the temperature of the coil unit above the prohibition temperature.
The controller preferably limits an operation of the coil unit when the temperature of the coil unit is at or above a predetermined limit temperature. Furthermore, the controller carries out sequentially an operation for prohibiting energization of the coil unit and an operation for permitting energization of the coil unit, thereby limiting the operation of the coil unit. Although an abnormal increase in the temperature of the coil unit is prevented, the above-described arrangement can eliminate a case where the coil unit cannot be operated for a long period of time.
When refrigerators are on display in a store or shop, visitors sometimes operate the door opening device repeatedly many times for confirmation of the performance of the apparatus. Thus, the frequency in the energization to the coil unit is rendered higher in the refrigerators on display in the store than those used in households and accordingly, there is a possibility that the temperature of the coil unit is abnormally increased. In view of this problem, the controller preferably carries out a store display mode in which the controller carries out sequentially an operation for prohibiting energization of the coil unit and an operation for permitting energization of the coil unit. Consequently, an abnormal increase in the temperature of the coil unit can be prevented in the door opening device incorporated in the refrigerator on display in the store.